We propose to continue a study of the morphogenesis of bacteriophage lambda and structure and its DNA. Specifically, the completion of phage heads in vitro will be examined, the mechanism and proteins responsible for the maturation of lambda DNA leading to molecules of proper size with cohesive single stranded ends will be sought and the reactivity of DNA in phage heads will be studied both to learn the effect of DNA condensation on its availability for reaction with mutagens and to explore the use of availability as a probe of how the DNA is arranged in the head. The goal is to provide a knowledge of how large macrostructures are formed and how DNA is condensed or closely packed.